title: Decreased motor unit discharge rate in the potentiated human tibialis anterior muscle.
abstract: OBJECTIVE
  The purpose of this study was to examine the influence of post-activation potentiation (PAP), the transient increase in low-frequency isometric force observed after muscle activity, on motor unit discharge rates measured during submaximal contractions.
  
  
  METHODS
  A quadrifilar needle electrode was inserted into the tibialis anterior muscle to determine discharge rate of individual motor units while monopolar electrodes were used to monitor the root-mean-square (RMS) and mean power frequency (MPF) of the surface EMG signal. Control (unpotentiated) and experimental (potentiated) measures were obtained during a 5 s voluntary contraction at 50% of maximal. In between these measures, subjects performed a 10 s maximal voluntary contraction (MVC) to induce PAP.
  
  
  RESULTS
  All subjects data are reported as means ± SEM (n = 10). Compared to baseline values measured prior to the MVC, isometric twitch force measured immediately after the MVC was increased by 260 ± 16% (day 3). Motor unit discharge rate in the potentiated tibialis anterior muscle decreased by approx. 10%, from 20.3 ± 0.8 (before) to 18.3 ± 0.99 pps (P = 0.01) (after). Moreover, the MPF was decreased by approx. 9% (from 58.1 ± 2.84 to 53.6 ± 2.85 Hz; P = 0.01) in the potentiated tibialis anterior. On the other hand, consistent with the absence of fatigue during the MVC, the RMS signal was not altered in the potentiated tibialis anterior (0.29 ± 0.03 vs. 0.33 ± 0.04 mV; P = 0.07).
  
  
  CONCLUSIONS
  Motor unit discharge rates determined during a brief, submaximal contraction were decreased in the potentiated human tibialis anterior muscle.
authors.affiliation: Electromyographic Kinesiology Laboratory, Faculty of Applied Health Sciences, Brock University, St Catharine's, ON, Canada.
authors.forename: J G
authors.initials: JG
authors.lastname: Inglis
authors.forename: J
authors.initials: J
authors.lastname: Howard
authors.forename: K
authors.initials: K
authors.lastname: McIntosh
authors.forename: D A
authors.initials: DA
authors.lastname: Gabriel
authors.forename: R
authors.initials: R
authors.lastname: Vandenboom
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D007866:Leg / Q000033:anatomy & histology; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D055815:Young Adult